Transmitting type secondary electron surface and electron tube

ABSTRACT

A transmission secondary electron emitter is provided which emits secondary electrons generated by the incidence of primary electrons. The transmission secondary electron emitter includes a secondary electron emitting layer which is made of diamond or a material containing diamond as a main component, and of which one surface is the surface of incidence for making the primary electrons incident thereon, and the other surface is the surface of emission for emitting the secondary electrons. Also included is a voltage applying arrangement for applying a predetermined voltage between the surfaces of the incidence and the emission of the secondary electron emitting layer to form an electric field in the secondary electron emitting layer.

This Application is a National Phase Application under 35 U.S.C. 371claiming the benefit of PCT/JP03/01992 filed on Feb. 24, 2003, which haspriority based on Japan Application No. 2002-64165 filed on Mar. 08,2002.

FIELD OF THE ART

The present invention relates to a transmission secondary electronemitter emitting secondary electrons generated by primary electrons madeincident, and an electron tube provided with the transmission secondaryelectron emitter.

BACKGROUND ART

Attention has been recently focused on a secondary electron emitterwhich is used for an electron tube and uses diamond. The reason for thisis that the diamond has negative electron affinity, and the diamond hashigh secondary electron-emission efficiency. One example is reported in“Thin Solid Films 253(1994) p 151.” In the example, the diamond is usedas a material for a reflection type secondary electron emitter of whichthe surface of emission for emitting secondary electrons is the same asthe surface of incidence for making primary electrons incident thereon.That is, in the secondary electron emitter, a polycrystalline diamondthin film of which the surface is terminated with hydrogen is formed ona substrate made of Mo, Pd, Ti or AlN or the like, and the emissionefficiency of the second electron is improved.

DISCLOSURE OF THE INVENTION

Since the surface of the incidence is the same as the surface of theemission in the above reflection type secondary electron emitter, thechange in the surface condition such as the desorption of hydrogentermination is caused by the primary electrons made incident, andthereby the emission efficiency of the secondary electron is lowered. Inorder to solve this drawback, a transmission secondary electron emitterof which the surface of the incidence is different from the surface ofthe emission is disclosed (Japanese Patent Application Laid-Open No.H10-144251 and U.S. Pat. No. 5,986,387).

FIG. 11 is a construction view illustrating an embodiment of an electrontube provided with a conventional transmission secondary electronemitter. The electron tube is provided with a cathode 101 having aphotoelectron emission surface, a transmission secondary electronemitter 102, and an anode 103. The transmission secondary electronemitter 102 comprises a diamond thin film 102 a, and a reinforcing means102 b for reinforcing the rigidity thereof. Herein, when photoelectronsare emitted from the cathode 101 by the incidence of light, thephotoelectrons are made incident on the secondary electron emitter 102to generate secondary electrons, and the secondary electrons are emittedto the anode 103. A fluorescent substance 103 a coated on a glasssurface plate 103 b emits light by the secondary electrons made incidenton the anode 103.

As shown in FIG. 12, a transmission secondary electron emitter is alsodisclosed, which uses diamond and makes secondary electrons accelerateby applying a voltage to an anode facing the surface of emission of asecondary electron emitter (U.S. Pat. No. 6,060,839). When primaryelectrons pass through an electrode 105, and are made incident on adiamond thin film 106 in the transmission secondary electron emitter,the secondary electrons are generated, and emitted. The secondaryelectrons are accelerated in the direction of the anode 107 by theelectric field formed by applying a voltage to the anode 107.

However, the above transmission secondary electron emitter has not hadthe practical emission efficiency of secondary electrons. This is aresult of the following reasons. That is, the secondary electronsgenerated by the incidence of the primary electrons are moved to thesurface of the emission of the side opposite to the surface of theincidence on the transmission secondary electron emitter, and thesecondary electrons should be emitted from the surface thereof. To thatend, a diamond film of which the film thickness is the diffusion length(mean free path) of the electron and which is very thin is required.

The experimental result of photoelectron emission by the presentinventor has shown that the diffusion length of the electron in thediamond film is about 0.05 μm. Therefore, it is necessary to adjust thefilm thickness of the diamond thin film to the same level as thediffusion length, that is, about 0.05 μm in order to emit the secondaryelectrons efficiently on the transmission secondary electron emitter.However, it is actually difficult to achieve the above transmissionsecondary electron emitter because of a deficiency in the mechanicalstrength and poor uniformity of the diamond film having a very thinthickness.

On the other hand, though the film thickness of at least several μm isrequired for sufficient mechanical strength of the diamond thin film,the secondary electrons generated by the incidence of the primaryelectrons hardly reach the surface of the emission of the side oppositeto the surface of the incidence in the thick film. Therefore, theemission efficiency of the secondary electron is remarkably lowered as aresult, and the practical transmission secondary electron emitter cannotbe achieved.

The present invention has been made to solve the aforementionedproblems. It is an object of the present invention to provide atransmission secondary electron emitter which can emit the secondaryelectrons efficiently for the incidence of the primary electrons, and anelectron tube using the same.

In order to achieve the aforementioned object, the transmissionsecondary electron emitter according to the present invention whichemits secondary electrons generated by the incidence of primaryelectrons, the transmission secondary electron emitter comprises: asecondary electron emitting layer which is made of diamond or a materialcontaining diamond as a main component, and of which one surface is thesurface of incidence for making the primary electrons incident thereon,and the other surface is the surface of emission for emitting thesecondary electrons; and a voltage applying means for applying apredetermined voltage between the surfaces of the incidence and theemission of the secondary electron emitting layer.

According to the above construction, the transmission secondary electronemitter has a transmission construction in which one surface of thesecondary electron emitting layer is the surface of the incidence, andthe other surface is the surface of the emission. Thereby theconstruction prevents the change in the surface condition of the surfaceof the emission by the incidence of the primary electrons, and thedecrease in the emission efficiency of the secondary electrons can beprevented. The secondary electron emitting layer is made of diamond or amaterial containing diamond as a main component, and thereby theemission efficiency of the secondary electrons according to the primaryelectrons can be improved. The voltage applying means forms the electricfield in the secondary electron emitting layer. Thereby the secondaryelectrons reach the surface of the emission easily, and the secondaryelectrons can be emitted with high efficiency.

The electron tube according to the present invention comprises: theabove transmission secondary electron emitter; an electron source foremitting the primary electrons to the transmission secondary electronemitter; an anode for collecting secondary electrons emitted from thetransmission secondary electron emitter; and an envelope foraccommodating the transmission secondary electron emitter, the electronsource, and the anode. The use of the transmission secondary electronemitter for the electron tube provides an electron tube which canefficiently obtain the secondary electrons from the incidence of theprimary electrons.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cross-sectional view illustrating the construction of atransmission secondary electron emitter according to the firstembodiment of the present invention.

FIG. 2 is a perspective view of the transmission secondary electronemitter shown in FIG. 1.

FIGS. 3A to 3E are process charts illustrating the manufacturing processof the transmission secondary electron emitter shown in FIG. 1.

FIG. 4 is a side cross-sectional view illustrating the construction ofthe transmission secondary electron emitter according to the secondembodiment.

FIG. 5 is a side cross-sectional view illustrating the construction ofthe transmission secondary electron emitter according to the thirdembodiment.

FIGS. 6A and 6B illustrate the construction of the transmissionsecondary electron emitter according to the fourth embodiment; FIG. 6Ais a side cross-sectional view, and FIG. 6B is a bottom view.

FIG. 7 is a sectional view schematically illustrating the constructionof an embodiment of a photomultiplier tube as the first embodiment of anelectron tube.

FIG. 8 is a sectional view schematically illustrating the constructionof another embodiment of a photomultiplier tube as the second embodimentof an electron tube.

FIG. 9 is a sectional view schematically illustrating the constructionof an image intensifier tube as the third embodiment of an electrontube.

FIG. 10 is a sectional view schematically illustrating the constructionof a plane display device as the fourth embodiment of an electron tube.

FIG. 11 is a construction view illustrating an embodiment of an electrontube provided with a conventional transmission secondary electronemitter.

FIG. 12 is a construction view illustrating another embodiment of aconventional transmission secondary electron emitter.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the preferred embodiments of the transmission secondaryelectron emitter and the electron tube according to the presentinvention will be described in detail with reference to the drawings. Inthe explanation of drawings, elements identical to each other will bereferred to with numerals identical to each other without overlappingdescriptions. The measurement ratio of the drawings does not necessarilycorrespond to that of the description.

FIG. 1 is a side cross-sectional view illustrating the construction of atransmission secondary electron emitter according to the firstembodiment of the present invention. FIG. 2 is a perspective view of thetransmission secondary electron emitter shown in FIG. 1.

A transmission secondary electron emitter illustrated in FIG. 1comprises a secondary electron emitting layer 1, a supporting frame 21,a first electrode 31 and a second electrode 32. In the transmissionsecondary electron emitter, secondary electrons are generated in thesecondary electron emitting layer 1 by an incidence of primaryelectrons, and secondary electrons are emitted outside. The transmissionsecondary electron emitter has a transmission type construction. Onesurface (an upper surface in FIG. 1) of the secondary electron emittinglayer 1 is the surface of the incidence for making the primary electronsincident thereon, and the other surface (a lower surface in FIG. 1) ofthe side opposite thereto is the surface of the emission for emittingthe secondary electrons.

The secondary electron emitting layers 1 are made of a diamond filmformed by diamond or a material containing diamond as a main component.It is preferable that the secondary electron emitting layer 1 is formedto be sufficiently thicker than the incidence depth of the primaryelectrons. It is preferable that the surface of the emission of thesecondary electron emitting layer 1 is terminated with hydrogen oroxygen.

The supporting frame 21 is a supporting means for reinforcing themechanical strength of the secondary electron emitting layer 1 formedthinly. The supporting frame 21 is made of a material such as Si, and isarranged on the outer edge part of the surface of the emission of thesecondary electron emitting layer 1.

The first electrode 31 formed on the surface of the incidence of thesecondary electron emitting layer 1 is an electrode of an incidentsurface side. As shown in FIG. 2, in this embodiment, the firstelectrode 31 is formed in a lattice shape on the surface of theincidence of the secondary electron emitting layer 1. The secondelectrode 32 formed on the surface of the emission of the secondaryelectron emitting layer 1 is an electrode of an emission surface side.In this embodiment, the second electrode 32 is formed on the wholesurface of the side opposite to the secondary electron emitting layer 1of the supporting frame 21. The first electrode 31 and the secondelectrode 32 are arranged as a voltage applying means for applying avoltage between the surfaces of the incidence and the emission of thesecondary electron emitting layer 1 to form an electric field in thesecondary electron emitting layer 1.

An active layer 11 for lowering the work function of the surface of theemission is formed on the surface of the emission of the secondaryelectron emitting layer 1.

In the above construction of the transmission secondary electronemitter, when the primary electrons are made incident on the surface ofincidence of the secondary electron emitting layer 1, the secondaryelectrons corresponding to the incident energy of the primary electronsare generated in the secondary electron emitting layer 1. An electricfield in which the side of the surface of the emission is positive andthe side of the surface of the incidence is negative is formed in thesecondary electron emitting layer 1, by applying a predetermined voltageusing a power supply 33 connected between the first electrode 31 and thesecond electrode 32. The secondary electrons generated in the secondaryelectron emitting layer 1 are accelerated in the direction to thesurface of the emission by the electric field. After the secondaryelectrons reach the surface of the emission, the secondary electronspass through the active layer 11, and are emitted outside of thetransmission secondary electron emitter.

The transmission secondary electron emitter of this embodiment canachieve the following effects.

The transmission secondary electron emitter shown in FIG. 1 has atransmission type construction in which one surface of the secondaryelectron emitting layer 1 is the surface of the incidence and the othersurface is the surface of the emission. Thus, the change in the surfacecondition of the surface of the emission due to the incidence of theprimary electrons is prevented not by the reflection type constructionin which the surface of incidence on which the primary electrons aremade incident is the surface of emission on which the secondaryelectrons are emitted, but by the transmission type construction. As aresult, since the change in the work function on the surface of theemission is suppressed, the decrease in the emission efficiency of thesecondary electrons can be prevented.

The secondary electron emitting layer 1 is formed by using diamond or amaterial containing diamond as a main component. Since the diamond hasnegative electron affinity, the diamond has a high emission efficiencyof the secondary electrons. Therefore, the secondary electron emittinglayer 1 can emit the secondary electrons efficiently for the incidenceof the primary electrons.

The first electrode 31 is formed on the side of the surface of theincidence of the secondary electron emitting layer 1, and the secondelectrode 32 is formed on the side of the surface of the emission.Thereby, the electric field is formed in the secondary electron emittinglayer 1. This can make the secondary electrons generated in thesecondary electron emitting layer 1 reach the surface of the emissionefficiently, and thereby the efficiency for emitting the secondaryelectrons outside of the transmission secondary electron emitter can beimproved.

Usually, it is necessary to form the thickness of the secondary electronemitting layer 1 to the same extent as the diffusion length (mean freepath) of the secondary electrons for emitting the secondary electronsgenerated in the secondary electron emitting layer 1 outside of thesecondary electron emitting layer 1. However, it is difficult to formthe secondary electron emitting layer 1 having such a thickness asdiamond and a diamond film containing diamond as a main component.

Correspondingly, in the transmission secondary electron emitter of thisembodiment, the electric field is formed in the secondary electronemitting layer 1, and the secondary electrons generated in the secondaryelectron emitting layer 1 are accelerated to the surface of theemission. Even when the thickness of the secondary electron emittinglayer 1 is thicker than the diffusion length, several μm for example,the secondary electrons can be efficiently emitted.

Herein, it is preferable to use polycrystalline diamond or a materialcontaining polycrystalline diamond as a main component as the materialof the secondary electron emitting layer 1. Since the polycrystallinediamond is made of granular crystals, the polycrystalline diamond hasgrain boundary faces as the surfaces of the granular crystals. Thesecondary electrons are emitted from the grain boundary faces existingin all directions that the secondary electrons generated in thesecondary electron emitting layer 1 diffuse.

Therefore, in the polycrystalline diamond, the distance from thegeneration of the secondary electrons to the emission thereof isshortened, and the number of the secondary electrons emitted increases.As a result, the higher emission efficiency can be obtained. Also, thepolycrystalline diamond can be produced in a large volume at low cost incomparison with monocrystalline diamond. If the polycrystalline diamondis used as a material of the secondary electron emitting layer 1, themanufacturing cost of the transmission secondary electron emitter can besuppressed.

The supporting frame 21 is arranged as a supporting means on the outeredge part of the surface of the emission of the secondary electronemitting layer 1. Since the secondary electron emitting layer 1 isthinly formed for emitting the secondary electrons generated in thesecondary electron emitting layer 1, the secondary electron emittinglayer 1 may have an insufficient mechanical strength. Thus, when it isnecessary to reinforce the mechanical strength of the secondary electronemitting layer 1, it is preferable that the supporting means such as thesupporting frame 21 is arranged at a suitable position such as the outeredge part of the surface of the emission. As a result, the mechanicalstrength of secondary electron emitting layer 1 can be reinforced.

The surface of the emission of the secondary electron emitting layer 1is preferably terminated with oxygen. The surface of the emission of thesecondary electron emitting layer 1 is terminated with oxygen, andthereby the surface of the emission of the secondary electron emittinglayer 1 is stabilized, and the electrical property can be retained for along time. The surface of the emission of the secondary electronemitting layer 1 may be terminated with hydrogen. Even when the surfaceof the emission is terminated with hydrogen, the work function of thesurface of the emission of the secondary electron emitting layer 1 canbe lowered, and the secondary electrons which reach the surface of theemission can be easily emitted outside of the transmission secondaryelectron emitter.

When the secondary electron emitting layer 1 is made of polycrystallinediamond or a material containing polycrystalline diamond as a maincomponent, the surface and the grain boundary faces of thepolycrystalline diamond of the secondary electron emitting layer 1 arepreferably terminated with oxygen. The surface of the emission of thesecondary electron emitting layer 1 is stabilized by terminating thesurface and the grain boundary faces with oxygen, and the electricalproperty can be retained for a long time.

Since the transmission secondary electron emitter shown in FIG. 1 has atransmission type construction, the primary electrons are not madeincident on the surface of the emission, and the surface condition dueto the above terminal process is not changed. As a result, the emissionefficiency of the secondary electrons improved by the terminal processcan be maintained.

It is preferable that the active layer 11 which lowers the work functionof the diamond is formed on the surface of the emission of the secondaryelectron emitting layer 1. The secondary electrons which reach thesurface of the emission of the secondary electron emitting layer can bemore easily emitted from the surface of the emission of the secondaryelectron emitting layer 1 by lowering the work function of the surfaceof the emission of the secondary electron emitting layer 1. The aboveeffect can be suitably achieved by forming the active layer by using analkali metal, an oxide of the alkali metal, or a fluoride of the alkalimetal or the like.

A process for manufacturing the transmission secondary electron emittershown in FIG. 1 and one example of a specific construction will bedescribed. FIG. 3A to FIG. 3E are process charts illustrating themanufacturing process of the transmission secondary electron emittershown in FIG. 1.

The secondary electron emitting layer 1 made of the polycrystallinediamond is deposited by about 5 μm thickness on one surface of asubstrate 20 made of Si (FIG. 3A). Synthesis methods by a chemical vapordeposition method (CVD method) using a heat filament or a micro waveplasma and a laser ablation method or the like can be used as a methodfor forming the layer of the thin polycrystalline diamond. The materialof the substrate 20 is not limited to Si. High melting metals such asmolybdenum and tantalum, and quartz and sapphire may be used.

The second electrode 32 is then formed on the other surface of thesubstrate 20 by evaporation (FIG. 3B). A part of the second electrode 32and the substrate 20 is removed by etching using a mask of anappropriate dimension from the other surface of the substrate 20, andthe secondary electron emitting layer 1 is partially exposed (FIG. 3C).The etching is executed by a HF+HNO₃ solution or a KOH solution. Whenthe substrate 20 is etched, and the secondary electron emitting layer 1is exposed, the etching is automatically stopped. A part which has notbeen removed by etching in the substrate 20 has a function forreinforcing the mechanical strength of the secondary electron emittinglayer 1 as the supporting frame 21.

A lattice-shaped first electrode 31 of an appropriate dimension isformed on the surface (the surface of the incidence) of the sideopposite to the surface (the surface of the emission) of the secondaryelectron emitting layer 1 exposed by the etching using aphotolithographic technique and a lift-off technique (FIG. 3D). Afterthese are maintained in vacuum, and the surface of the emission of thesecondary electron emitting layer 1 is cleaned, the surface of theemission or the like is terminated with oxygen or hydrogen.

Finally, a material having a property for lowering the work function ofthe surface of the diamond such as an alkali metal, an oxide of thealkali metal, and a fluoride of the alkali metal is coated on thesurface of the emission of the secondary electron emitting layer 1 toform the active layer 11 (FIG. 3E).

The transmission secondary electron emitter of the first embodiment canbe produced by the above manufacturing process. However, the process formanufacturing the transmission secondary electron emitter and thespecific construction thereof are not limited to the example, andvarious processes and the constructions can be used.

FIG. 4 is a side cross-sectional view illustrating the construction ofthe transmission secondary electron emitter according to the secondembodiment.

The transmission secondary electron emitter shown in FIG. 4 comprisesthe secondary electron emitting layer 1, the active layer 11, thesupporting frame 21, a first electrode film 31 a, an auxiliary electrode34 and the second electrode 32. Of these, the constructions of thesecondary electron emitting layer 1, the active layer 11, the supportingframe 21 and the second electrode 32 are identical to those of thetransmission secondary electron emitter shown in FIG. 1.

The first electrode film 31 a is formed in the film state on the surfaceof the incidence of the secondary electron emitting layer 1. The firstelectrode film 31 a is very thinly formed (the thickness of about 30 to150 Å) such that the secondary electrons generated in the secondaryelectron emitting layer 1 are not absorbed by the first electrode film31 a. The auxiliary electrode 34 is formed at the predetermined positionon the first electrode film 31 a for the electric connection to thefirst electrode film 31 a formed in the film state.

The transmission secondary electron emitter of this embodiment has atransmission type construction. One surface of the secondary electronemitting layer 1 are the surface of the incidence, and the other surfaceis the surface of the emission. This construction prevents the change inthe surface condition of the surface of the emission, and the decreasein the discharge efficiency of the secondary electrons can be prevented.Since the secondary electron emitting layers 1 is formed by usingdiamond or a material containing diamond as a main component, thesecondary electron emitting layer 1 can emit the secondary electronswith high efficiency for the incidence of the primary electrons.

The first electrode film 31 a and the second electrode 32 arerespectively formed on the side of the surface of the incidence of thesecondary electron emitting layer 1 and on the side of the surface ofthe emission, and thereby the electric field is formed in the secondaryelectron emitting layer 1. The electric field is formed in the secondaryelectron emitting layer 1, and the secondary electrons generated in thesecondary electron emitting layer 1 are accelerated to the surface ofthe emission. Thereby the secondary electrons can be efficiently emittedoutside of the transmission secondary electron emitter.

The first electrode film 31 a is formed in the thin film state on thesurface of the incidence of the secondary electron emitting layer 1.Though the transmission secondary electron emitter can be suitablyoperated by forming the electrode which is in contact with the secondaryelectron emitting layer 1 among the electrodes composing the voltageapplying means as is the case with the first electrode 31 shown in FIG.1, the electrodes are preferably formed in the film state as shown inFIG. 4 by methods such as a deposition when it is necessary to make themanufacturing process simple.

In this case, the voltage applying means for improving the emissionefficiency of the secondary electrons of the transmission secondaryelectron emitter can be arranged by a simplified process. The primaryelectrons can reach the secondary electron emitting layer 1 withoutbeing absorbed to the first electrode film 31 a by forming the firstelectrode film 31 a very thinly as described above.

FIG. 5 is a side cross-sectional view illustrating the construction ofthe transmission secondary electron emitter according to the thirdembodiment.

The transmission secondary electron emitter shown in FIG. 5 comprisesthe secondary electron emitting layer 1, the active layer 11, asupporting frame 22, a first electrode 35 and a second electrode 36. Ofthese, the constructions of the secondary electron emitting layer 1 andthe active layer 11 are identical to those of the transmission secondaryelectron emitter shown in FIG. 1.

The supporting frame 22 is a supporting means for reinforcing themechanical strength of the secondary electron emitting layer 1 formedthinly. The supporting frame 22 is arranged on the outer edge part ofthe surface of the incidence of the secondary electron emitting layer 1.

The first electrode 35 formed on the surface of the incidence of thesecondary electron emitting layer 1 is an electrode of an incidentsurface side. In this embodiment, the first electrode 35 is formed onthe whole surface of the side opposite the secondary electron emittinglayer 1 of the supporting frame 22. The second electrode 36 formed onthe surface of the emission of the secondary electron emitting layer 1is an electrode of an emission surface side. In this embodiment, asecond electrode 36 is formed in a lattice shape on the surface of theemission of the secondary electron emitting layer 1. The first electrode35 and the second electrode 36 are arranged as voltage applying meansfor applying a voltage between the surfaces of the incidence and theemission of the secondary electron emitting layer 1 to form an electricfield in the secondary electron emitting layer 1.

The transmission secondary electron emitter of this embodiment has atransmission type construction. One surface of the secondary electronemitting layer 1 is the surface of the incidence, and the other surfaceis the surface of the emission. The construction prevents the change inthe surface condition of the surface of the emission, and the decreasein the discharge efficiency of the secondary electrons can be prevented.Since the secondary electron emitting layers 1 are formed by usingdiamond or a material containing diamond as a main component, thesecondary electron emitting layer 1 can emit the secondary electronsefficiently for the incidence of the primary electrons.

The first electrode 35 is formed on the side of the surface of theincidence of the secondary electron emitting layer 1, and the secondelectrode 36 is formed on the side of the surface of the emission.Thereby, the electric field is formed in the secondary electron emittinglayer 1. The electric field is formed in the secondary electron emittinglayer 1, and the secondary electrons generated in the secondary electronemitting layer 1 are accelerated to the surface of the emission. Therebythe secondary electrons can be efficiently emitted outside of thetransmission secondary electron emitter.

A supporting frame 22 is arranged as a supporting means at the outeredge part of the surface of the incidence of the secondary electronemitting layer 1. When it is necessary to reinforce the mechanicalstrength of the secondary electron emitting layer 1 formed thinly, thesupporting means is arranged on the surface of the incidence in thisembodiment, in addition to the surface of the emission as shown in FIG.1, and thereby the mechanical strength of the secondary electronemitting layer 1 is suitably reinforced.

FIG. 6A and FIG. 6B illustrate the construction of the fourth embodimentof the transmission secondary electron emitter. FIG. 6A is a sidecross-sectional view of the transmission secondary electron emitter, andFIG. 6B is a bottom view of the transmission secondary electron emitterseen from the side of the second electrode 32.

The transmission secondary electron emitter shown in FIG. 6A and FIG. 6Bcomprises the secondary electron emitting layer 1, the active layer 11,a supporting frame 23, a first electrode 31 and a second electrode 32.Of these, the constructions of the secondary electron emitting layer 1,the active layer 11 and the first electrode 31 are identical to those ofthe transmission secondary electron emitter shown in FIG. 1.

As shown in FIG. 6B, the supporting frame 23 is arranged in a latticeshape on the surface of the emission of the secondary electron emittinglayer 1. The supporting frame 23 is formed such that the shape and areaof each latticed frame are uniform. A second electrode 32 is formed onthe whole surface of the side opposite the secondary electron emittinglayer 1 of the supporting frame 23 arranged in a lattice shape.

The transmission secondary electron emitter of this embodiment has atransmission type construction in which one surface of the secondaryelectron emitting layer 1 is the surface of the incidence and the othersurface is the surface of the emission. This prevents the change in thesurface condition of the surface of the emission, and the decrease inthe discharge efficiency of the secondary electrons can be prevented.The secondary electron emitting layer 1 is formed by using diamond or amaterial containing diamond as a main component. Thereby the secondaryelectron emitting layer 1 can emit the secondary electrons efficientlyfor the incidence of the primary electrons.

The first electrode 31 is formed on the side of the surface of theincidence of the secondary electron emitting layer 1, and the secondelectrode 32 is formed on the side of the surface of the emission.Thereby, the electric field is formed in the secondary electron emittinglayer 1. The electric field is formed in the secondary electron emittinglayer 1, and the secondary electrons generated in the secondary electronemitting layer 1 are accelerated to the surface of the emission. Therebythe secondary electrons can be efficiently emitted outside of thetransmission secondary electron emitter.

The supporting frame 23 for reinforcing the mechanical strength of thesecondary electron emitting layer 1 is arranged in a lattice shape. Whenthe area of the secondary electron emitting layer 1 is comparativelysmall, the strength of the secondary electron emitting layer can besufficiently reinforced by the support means having the shape shown inFIG. 1. However, the mechanical strength of the secondary electronemitting layer 1 can be further reinforced by arranging the supportingmeans having the shape of this embodiment when the area of the secondaryelectron emitting layer 1 is large and it is necessary to reinforce themechanical strength of the secondary electron emitting layer 1 further.

At this time, when the supporting frame 23 is formed such that the shapeand area of each latticed frame are uniform, the mechanical strength ofthe supporting frame 23 can be increased. The shape of the supportingmeans is not limited to the lattice shape, and the supporting frame 23having various shapes may be used.

Though the second electrode 36 and the first electrode 31 are formed ina lattice shape in the third and fourth embodiments of the transmissionsecondary electron emitter, the electrodes may be formed in a thin filmform as is the case with the first electrode film 31 a in the secondembodiment. The lattice shape, the thin film shape, or another shape canbe properly selected as the shape of the electrode arranged on thesurface of the secondary electron emitting layer 1.

The transmission secondary electron emitter described above can be usedfor electron tubes such as a photomultiplier tube and an imageintensifier tube. The embodiment of the electron tube will be describedas follows.

FIG. 7 is a sectional view schematically illustrating the constructionof an embodiment of a photomultiplier tube as the first embodiment of anelectron tube according to the present invention.

The photomultiplier tube shown in FIG. 7 comprises a photocathode 41which converts light to be detected into photoelectrons and emits thephotoelectrons, a transmission secondary electron emitter 5 whichintensifies the photoelectron as the secondary electrons, an anode 6 forcollecting secondary electrons intensified, and a vacuum envelope 7accommodating them under a vacuum condition. The photocathode 41, thetransmission secondary electron emitter 5 and the anode 6 are arrangedat a predetermined interval in order from the side of the incidence ofthe light to be detected in the vacuum envelope 7.

The photocathode 41 is an electron source which emits the photoelectronsas the primary electrons to the transmission secondary electron emitter5. In this embodiment, a transmission type photocathode is used, whereinthe surface on which the light to be detected is made incident isdifferent from the surface from which the photoelectrons are emitted.The reflection type photocathode may be used in addition to thetransmission type photocathode 41.

The transmission secondary electron emitter 5 is formed at apredetermined distance from the photocathode 41. The above transmissionsecondary electron emitter which is made of diamond or a materialcontaining diamond as a main component is used as the transmissionsecondary electron emitter 5. The transmission secondary electronemitter makes the photoelectrons emitted from the photocathode 41incident from the surface of incidence as the primary electrons, and thesecondary electrons are intensified. The secondary electrons are thenemitted from the surface of the emission of the side opposite thesurface of incidence. The anode 6 is arranged at a predetermineddistance from the surface of the emission of the transmission secondaryelectron emitter 5. The anode 6 collects the secondary electrons emittedfrom the transmission secondary electron emitter 5.

The photocathode 41, the transmission secondary electron emitter 5 andthe anode 6 are involved in the vacuum envelope 7 as an airtightcontainer which is in the vacuum state. An entrance window 71 is formedon the surface on which the light to be detected is made incident, andwhich faces the photocathode 41 in the vacuum envelope 7. As a result,the light to be detected having a predetermined wavelength among thelight made incident is efficiently made incident on the photocathode 41.A voltage is gradually applied to the photocathode 41, the transmissionsecondary electron emitter 5 and the anode 6 to form the electric fieldsuch that the side of the photocathode 41 is an electronegativepotential and the side of the anode 6 is and electropositive potential.

When the light to be detected is made incident on the surface of theincidence of the photocathode 41 through the entrance window 71 in theabove construction, the photoelectrons as the primary electrons aregenerated on the photocathode 41, and emitted in the vacuum of thevacuum envelope 7 from the surface of the emission. The electric fieldis formed by applying a voltage to the surface of the incidence of thetransmission secondary electron emitter 5, a positive voltage relativeto the photocathode 41. The photoelectrons emitted in the vacuum areaccelerated, and made incident on the transmission secondary electronemitter 5.

The photoelectrons are intensified by corresponding to acceleration bythe electric field on the transmission secondary electron emitter 5, andbecome the secondary electrons. The secondary electrons are emitted inthe vacuum again. The electric field is formed by applying a voltage tothe anode 6, a positive voltage relative to the surface of the emissionof the transmission secondary electron emitter 5, and the secondaryelectrons emitted from the transmission secondary electron emitter 5 arecollected in the anode 6. The secondary electrons are taken out outsideof the photomultiplier tube as a detecting signal due to the incidentlight to be detected.

The photomultiplier tube shown in FIG. 7 is provided with thetransmission secondary electron emitter 5 having the above construction.As a result, the secondary electrons can be efficiently obtained for thephotoelectrons (primary electrons), and the photomultiplier tube capableof detecting the light to be detected can be achieved at a highsecondary electronic multiplication factor. The high secondaryelectronic multiplication factor causes the accurate detection of thelight to be detected at a high S/N ratio.

FIG. 8 is a sectional view schematically illustrating the constructionof another embodiment of a photomultiplier tube as the second embodimentof an electron tube.

A photomultiplier tube shown in FIG. 8 comprises the photocathode 41,the transmission secondary electron emitter 5, the anode 6, and thevacuum envelope 7. Of these, the constructions of the photocathode 41,the anode 6 and the vacuum envelope 7 are identical to those of thephotomultiplier tube shown in FIG. 7.

In this embodiment, a plurality of transmission secondary electronemitters 5 (three pieces in FIG. 8) are used. The above transmissionsecondary electron emitter made of diamond or a material containingdiamond as a main component is used for a plurality of transmissionsecondary electron emitters 5. The plurality of transmission secondaryelectron emitters 5 are arranged at predetermined intervals such thatthe surfaces of incidence thereof face the surfaces of the emissionrespectively. The anode 6 is arranged at a predetermined distance fromthe surface of the emission of the transmission secondary electronemitter 5 at the furthermost position from the photocathode 41. Theanode 6 collects the secondary electrons emitted from the transmissionsecondary electron emitter 5.

When the light to be detected is made incident on the photocathode 41through the entrance window 71 in the above construction, thephotoelectrons are generated on the photocathode 41, and emitted in thevacuum of the vacuum envelope 7. The photoelectrons emitted in thevacuum is made incident on the transmission secondary electron emitter 5placed at the nearest position to the photocathode 41 as the primaryelectrons, and emitted as the intensified secondary electrons. Theelectrons are repeatedly intensified by a plurality of transmissionsecondary electron emitters 5 arranged afterwards. Finally, thesecondary electrons intensified are collected in the anode 6, and thesecondary electrons are taken out outside of the photomultiplier tube asthe detecting signal by the incident light to be detected.

In the photomultiplier tube shown in FIG. 8, the plurality oftransmission secondary electron emitters 5 having the above constructionare used, and thereby the photomultiplier tube capable of detecting thelight to be detected can be achieved at a higher secondary electronicmultiplication factor. As a result, the high secondary electronicmultiplication factor causes the accurate detection of the light to bedetected at higher S/N ratio.

Even when it is necessary to use a plurality of secondary electronemitters as in this embodiment, a plurality of second electron surfacescan be thinly stacked if the above transmission secondary electronemitter 5 is used.

Though the above photomultiplier tube of each embodiment has a so-calledadjacent type construction such that the photocathode 41 faces thetransmission secondary electron emitter 5 and the anode 6, thephotomultiplier tube may have a so-called electrostatic focusing typeconstruction such that an electrostatic lens is provided between thephotocathode 41 and the transmission secondary electron emitter 5, andthe photoelectrons are focused.

Though the anode 6 for collecting the secondary electrons is provided, asemiconductor element such as a photodiode may be provided instead ofthe anode 6. Each embodiment of the above photomultiplier tube can besuitably executed by bombarding the secondary electrons directly to thesemiconductor element, that is, by operating as a so-called electronbombardment type photomultiplier tube.

FIG. 9 is a sectional view schematically illustrating the constructionof an image intensifier tube as the third embodiment of an electrontube.

An image intensifier tube shown in FIG. 9 comprises the photocathode 41,the transmission secondary electron emitter 5, an anode 6 a, and thevacuum envelope 7. Of these, the constructions of the photocathode 41,the transmission secondary electron emitter 5 and the vacuum envelope 7are identical to those of the photomultiplier tube shown in FIG. 7.

The anode 6 a has a function for collecting the secondary electronsemitted from the transmission secondary electron emitter 5, and isarranged at a predetermined distance from the surface of the emission ofthe transmission secondary electron emitter 5. The anode 6 a has afluorescent screen including a fluorescent material emitting light bythe incidence of the electron.

When the light to be detected composing the image transmits the entrancewindow 71, and is made incident on the photocathode 41 in the aboveconstruction, the photoelectrons are generated in the photocathode 41,and are emitted in the vacuum envelope 7. The photoelectrons emitted aremade incident on the transmission secondary electron emitter 5. At thistime, the electric field is formed by applying a voltage to the surfaceof incidence of the transmission secondary electron emitter 5, apositive voltage relative to the photocathode 41. Since thephotoelectrons advance in parallel with the electric field, thephotoelectrons are made incident on the transmission secondary electronemitter 5 while keeping two dimensional information at the time of beingmade incident on the image intensifier tube.

The photoelectrons made incident on the transmission secondary electronemitter 5 are intensified, and are emitted as the secondary electrons.The secondary electrons are collected in the anode 6 a having afluorescent screen. At this time, a voltage is applied to the anode 6 a,a positive voltage relative to the surface of emission of thetransmission secondary electron emitter 5. As a result, the electricfield is formed on the anode 6 a, and the secondary electrons arecollected in the anode 6 a while keeping two dimensional informationthat the photoelectrons have. Thereby the fluorescent screen of theanode 6 a emits light. An image due to the light to be detected madeincident on the image intensifier tube is intensified by the aboveoperation, and is output from the fluorescent screen of the anode 6 a asthe image.

The image intensifier tube can be obtained, in which the secondaryelectrons can be efficiently obtained for the incidence of the light tobe detected by using the transmission secondary electron emitter 5having the above construction in the image intensifier tube shown inFIG. 9. As a result, the image having high luminance can be obtained,and the image can be accurately reproduced at high S/N ratio even if theimage incident is weak.

Though the fluorescent screen is used as a means for emitting light bythe secondary electrons in the above image intensifier tube, the meansshould at least convert the electrons into the image. For instance,similar effects can be achieved by providing an image pickup device suchas a charge coupled device (CCD) instead of the anode 6 a having thefluorescent screen, driving the secondary electrons directly to theimage pickup device, and imaging them.

FIG. 10 is a sectional view schematically illustrating the constructionof a plane display device as the fourth embodiment of an electron tube.

A plane display device shown in FIG. 10 is a field emission displaycomprising a field emission electron source array 42, the transmissionsecondary electron emitter 5, an anode 6 b and the vacuum envelope 7. Ofthese, the constructions of the transmission secondary electron emitter5 and the vacuum envelope 7 are identical to those of the imageintensifier tube shown in FIG. 9.

The anode 6 b has a function for collecting the secondary electrons, andis arranged at a predetermined distance from the surface of the emissionof the transmission secondary electron emitter 5. The anode 6 b has afluorescent screen including a fluorescent material emitting light bythe incidence of the electron. Pixels of RGB are arranged on thefluorescent screen, and the image is displayed by the incidence of theelectron.

The field emission electron source array 42 has a construction in whicha lot of field emission electron sources 43 are arranged in an array.The field emission electron sources 43 emit the electrons correspondingto the respective pixels of RGB of the image output in the plane displaydevice.

In the above construction, the electrons corresponding to respectivepixels of the image output are emitted from the field emission electronsource 43 to the vacuum envelope 7. The electrons emitted are madeincident on the transmission secondary electron emitter 5. At this time,the electric field is formed by applying a voltage to the surface of theincidence of the transmission secondary electron emitter 5, a positivevoltage relative to the field emission electron source array 42. Sincethe electrons advance in parallel with the electric field, the electronsare made incident on the transmission secondary electron emitter 5 whilekeeping two dimensional information at the time of being emitted fromthe field emission electron source 43.

The secondary electrons are generated and emitted by the electrons madeincident on the transmission secondary electron emitter 5, and arecollected in the anode 6 b having the fluorescent screen. At this time,a voltage is applied to the anode 6 b, a positive voltage relative tothe surface of emission of the transmission secondary electron emitter5. As a result, the electric field is formed on the anode 6 b, and thesecondary electrons are collected in the anode 6 b while keeping twodimensional information that the electrons have. A predetermined pixelemits light on the fluorescent screen of the anode 6 b. The electronscorresponding to respective pixels of the image output are emitted fromfield emission electron source 43 by the above operation, and thesecondary electrons generated on the transmission secondary electronemitter 5 make a fluorescent screen emit light. As a result, apredetermined image is output.

In the plane display device shown in FIG. 10, the secondary electronscan be efficiently obtained for the input of the electrons (primaryelectrons) by using the transmission secondary electron emitter 5 havingthe above construction, and the plane display device which makes thefluorescent screen emit light can be achieved. As a result, the outputof the image of the plane display device can be further made highluminance. Since ions generated by accelerating a large amount ofelectrons to the fluorescent screen and making the electrons incident onthe fluorescent screen do not reach the field emission element directly,the plane display device work is long-lived and can be stably operated.

Herein, a field emission electron source array 42 is provided, in whicha lot of field emission electron sources 43 are arranged in an array asthe electron source for emitting the electrons corresponding to theimage output in this embodiment. A gate electrode, a focusing electrodeor other electron sources can be used as the electron source used inthis embodiment in addition to the above electron source. As a result,the fluorescent display tube having the effects the same as the aboveplane display device can be achieved.

When it is necessary to use a plurality of secondary electron emittersin the image intensifier tube of the third embodiment and the planedisplay device of the fourth embodiment as is the case with thephotomultiplier tube of the above second embodiment, a plurality ofsecondary electron emitters can be thinly stacked by using the abovetransmission secondary electron emitter 5, and necessary brightness canbe obtained on the fluorescent screen.

The transmission secondary electron emitter and the electron tubeaccording to the present invention is not limited to the aboveembodiment, and various changes can be made. For instance, when themechanical strength of secondary electron emitting layer 1 is sufficientin each embodiment of the transmission secondary electron emitter, thesupporting frames 21–23 for reinforcing the mechanical strength may notbe provided. When the secondary electrons can be efficiently emittedfrom the secondary electron emitting layer 1, the active layer 11 forlowering the work function of the surface of the emission of thesecondary electron emitting layer 1 may not be arranged.

When it is necessary to reinforce the mechanical strength of the vacuumenvelope 7 for enlargement or the like in each embodiment of theelectron tube, a reinforcing means such as a spacer is preferablyprovided in the vacuum envelope 7 such as between the electron sourceand the transmission secondary electron emitter, and between thetransmission secondary electron emitter and the anode.

INDUSTRIAL APPLICABILITY

As has been described in detail above, the transmission secondaryelectron emitter and the electron tube according to the presentinvention achieve the following effects. The transmission secondaryelectron emitter can efficiently emit the secondary electrons forincidence of the primary electrons, and the electron tube use the same.That is, the transmission secondary electron emitter has a transmissionconstruction in which one surface of the secondary electron emittinglayer is the surface of incidence, and the other surface is the surfaceof emission. Thereby the construction prevents the change in the surfacecondition of the surface of the emission by the incidence of the primaryelectrons, and the decrease in the emission efficiency of the secondaryelectrons can be prevented.

The secondary electron emitting layer is made of diamond or a materialcontaining diamond as a main component, and thereby the secondaryelectrons can be emitted with high efficiency. The voltage applyingmeans forms the electric field in the secondary electron emitting layer.Thereby the secondary electrons reach the surface of emission easily,and the secondary electrons can be emitted with high efficiency.

The use of the transmission secondary electron emitter for the electrontube provides an electron tube which can efficiently obtain thesecondary electrons from the primary electrons of the electron source.

1. A transmission secondary electron emitter which emits secondaryelectrons generated by the incidence of primary electrons, thetransmission secondary electron emitter comprising: a secondary electronemitting layer which is made of diamond or a material containing diamondas a main component, and of which one surface is the surface ofincidence for making the primary electrons incident thereon from aposition outside of the secondary electron emitting layer, and the othersurface is the surface of emission for emitting the secondary electronscorresponding to the incident energy of the primary electrons andgenerated in the secondary electron emitting layer; and a voltageapplying means for applying a predetermined voltage between the surfacesof the incidence and the emission of the secondary electron emittinglayer, wherein the voltage applying means includes a first electrodeformed on the side of the surface of the incidence and a secondelectrode formed on the side of the surface of the emission for applyingthe predetermined voltage to form an electric field in the secondaryelectron emitting layer for accelerating the secondary electrons in thedirection to the surface of the emission.
 2. The transmission secondaryelectron emitter according to claim 1, further comprising a supportingmeans for reinforcing the mechanical strength of the secondary electronemitting layer.
 3. The transmission secondary electron emitter accordingto claim 1, wherein the secondary electron emitting layer is made ofpolycrystalline diamond or a material containing polycrystalline diamondas a main component.
 4. The transmission secondary electron emitteraccording to claim 3, wherein the surface and the grain boundary face ofthe polycrystalline diamond of the secondary electron emitting layer areterminated with oxygen.
 5. The transmission secondary electron emitteraccording to claim 1, wherein the surface of the emission of thesecondary electron emitting layer is terminated with hydrogen.
 6. Thetransmission secondary electron emitter according to claim 1, whereinthe surface of the emission of the secondary electron emitting layer isterminated with oxygen.
 7. The transmission secondary electron emitteraccording to claim 1, wherein an active layer for lowering the workfunction of the secondary electron emitting layer is formed on thesurface of the emission of the secondary electron emitting layer.
 8. Thetransmission secondary electron emitter according to claim 7, whereinthe active layer of the secondary electron emitting layer comprises analkali metal, an oxide of the alkali metal, or a fluoride of the alkalimetal.
 9. An electron tube comprising: the transmission secondaryelectron emitter according to claim 1; an electron source for emittingthe primary electrons to the transmission secondary electron emitter; ananode for collecting the secondary electrons emitted from thetransmission secondary electron emitter; and an envelope foraccommodating the transmission secondary electron emitter, the electronsource, and the anode.
 10. The electron tube according to claim 9,wherein the electron source includes a photocathode for emittingphotoelectrons excited by incident light to be detected as the primaryelectrons.
 11. The electron tube according to claim 9, wherein theelectron source includes a photocathode for emitting photoelectronsexcited by incident light to be detected as the primary electrons, andthe anode has a fluorescent screen emitting light by the incidence ofthe secondary electrons.
 12. The electron tube according to claim 9,wherein the electron source includes a field emission electron source,and the anode has a fluorescent screen emitting light by the incidenceof the secondary electrons.
 13. The electron tube according to claim 9,wherein the electron source includes a field emission electron sourcearray in which a plurality of field emission electron sources arearranged in an array, and the anode has a fluorescent screen emittinglight by the incidence of the secondary electrons.